1. Field of the Invention
The present invention relates to a novel liquid crystal device that can be used as a display device or color variable filter and can be applied in wide uses including consumer industrial merchandise, professional merchandise and communication merchandise, and an electronic apparatus using the same.
2. Description of the Related Art
The LCD (liquid crystal display device) which is an article using liquid crystal has recently been used widely in pocket calculator, clock, word processor, television receiver, etc.
From the technical point of view, the existing LCD's may be classified into two categories. One is a simple matrix driving method for driving the liquid crystal by time division, which is a simple structure formed by gluing a pair of light transmittable substrates forming plural band-shaped transparent electrodes respectively, and the other is an active matrix driving method for driving each picture element in a form apparently close to static driving, by adding nonlinear elements such as thin film transistor (TFT) and diodes to the display picture element parts. The display quality is superior in the latter active matrix driving method, but the former simple matrix driving method is advantageous in the aspect of cost.
Incidentally, the liquid crystal display mode is known as one of the important factors that determine the display quality. At the present, in the active matrix driving LCD, the so-called twisted nematic (TN) mode having a twisting of 90 degrees in the initial (non electric-field state) liquid crystal orientation is generally employed, and in the simple matrix driving type LCD, the super twisted nematic (STN) mode having the twisting angle of liquid crystal set somewhere between 180 degrees and 270 degrees is widely utilized.
In the latter STN mode, the method of putting a liquid crystal panel or phase difference film further on the liquid crystal device of STN mode (STN cell) for the purpose of optical compensation (known as DSTN method or FSTN method) is applied as display device for word processor and notebook type personal computer.
As another method, in a limited application range such as clock, the guest-host (GH) mode having a dichroic pigment added to the liquid crystal is known. This method is, as compared with the TN mode or STN mode, capable of presenting a bright display device of wide viewing angle, when considered by including the mode capable of displaying without requiring polarizer plate by applying a twisting to the liquid crystal orientation (White-Taylor type GH mode), but is inferior in contrast.
In these display modes developed hitherto, it is commonly demanded to enhance the response speed. By the improvements of liquid crystal material and cell composition, it is enhanced to scores to hundreds of milliseconds at the present, but it is not enough yet for display of moving pictures, especially in the display device using the so-called mouse system or applied merchandise where high speed optical shutter is indispensable.
To meet such needs, lately, liquid crystals possessing high speed response characteristics have been proposed. In one of them, asymmetric carbon is added to the liquid crystal molecular skeleton, and the liquid crystal expressing ferroelectric property thereby (a ferroelectric liquid crystal) is used. In this method, a ferroelectric liquid crystal is sealed over the liquid crystal panel having a gap of 1 to 2 .mu.m, and the display is offered by making use of birefringence property of the liquid crystal itself and the mutual interference of the polarity of applied voltage and molecular orientation of liquid crystal (surface stabilized ferroelectric liquid crystal: SSF-LC).
The SSF-LC possesses a responses speed of scores to hundreds of microseconds, and exhibits a high speed with a difference of several digits as compared with the conventional nematic liquid crystal, and also possesses memory characteristics, and hence it is expected as a display device of next generation.
However, it has its own disadvantages, such as vulnerability to mechanical impact, requirement of advanced technology in control of liquid crystal orientation, tendency of contrast drop when driving, and large dependence of characteristics on temperature, and it is far from the practical level at the present.
As another method, the liquid crystal/high-molecular compound film dispersing liquid crystal drops of micron size order in high molecular weight matrix is proposed. This is classified in two types depending on the method of manufacture, that is, liquid crystal drops are completely enclosed in the high molecular matrix to be in an isolated state in one type, while the liquid crystal is not isolated but is included in the three-dimensional reticular high molecule in the other type. In either type, since the liquid crystal is enclosed in a tiny space, the response characteristics of higher speed than before are realized, practically in the order to milliseconds.
FIG. 19 shows the principle of operation of the liquid crystal device of liquid crystal drops in an isolated state in the high molecular matrix. The liquid crystal device is composed of plural liquid crystal drops 17 interspaced between light transmittable substrates 15, 16 forming transparent electrodes on the confronting surfaces, respectively. An AC voltage from a power source 18 is selectively applied to the transparent electrodes of the light transmittable substrates 15,16 by a switch 19.
As shown in FIG. 19(a), in a non electric-field state, since the liquid crystal molecules are arranged irregularly in the liquid crystal space, and the incident light is scattered, and a white turbid state is recognized as a result.
However, when a sufficiently high voltage is applied, supposing the liquid crystal used herein possesses a positive dielectric anisotropy (.DELTA..epsilon.=.epsilon.a-.epsilon.b&gt;0, .epsilon.a: dielectric constant of liquid crystal molecule along the optical axis of liquid crystal molecule, .epsilon.b: dielectric constant normal to the optical axis, the orientation is re-aligned in the direction of electrolysis), so that a transparent state is obtained.
Thus, by application/elimination of voltage, the transparent/opaque state can be changed over at a speed in the order of milliseconds. This display mode, however, has its own problems in the display characteristics, such as difference in transmissivity in the ascending and descending stroke of voltage, that is, the hysteresis characteristics, and difficulty in elevation of resistance as liquid crystal panel.
In the display device or photo modulation device, liquid crystal device of high contrast and brightness (high transmissivity) and having response characteristics of high speed are desired.
From this point of view, as the liquid crystal display mode, between the display modes of using the polarizer plate and not using the polarizer plate, the latter display mode without requiring polarizer plate is more advantageous. That is, by using the polarizer plate, the optical utility is at least decreased below 50% due to the optical property of the polarizer plate itself. Therefore, as the display mode, the White-Taylor type GH mode twisting and orienting the material having pigments added to liquid crystal, and the liquid crystal/high-molecular compound film are considered.
In the White-Taylor type GH mode, it is known that the response speed in the order of microseconds can be obtained by increasing the angle of twisting orientation and orienting vertically on the substrate, but the shortcoming is that a high contrast cannot be obtained. On the other hand, it is reported that the contrast is reported by designing a two-layer type GH mode (PROC. of the SID, 25/4,1984, p. 275). In the two-layer type GH mode, however, since an ordinary glass substrate is used between liquid crystal layers, a parallax is caused in the upper and lower liquid crystal layers depending on the viewing angle, and the display may be blurry.
Meanwhile, in the display mode using liquid crystal/high-molecular compound film as shown in FIG. 19, there are basic problems such as hysteresis characteristic, difficulty in elevation of resistance of liquid crystal panel, poor reliability.